This application is based on Japanese Patent Application HEI 10-185109, filed on Jun. 30, 1998, the entire contents of which are incorporated herein by reference.
a) Field of the Invention
The present invention relates to manufacture techniques for semiconductor devices, and more particularly a manufacture method and system for a semiconductor device capable of forming a thin oxynitride film on the surface of a silicon wafer.
b) Description of the Related Art
Demands for higher integration and higher operation speed of CMOS semiconductor devices are high. In order to meet such requests, it is necessary to make finer transistors constituting CMOS devices and improve a driving force. In the case of a p-channel MOS transistor, it is necessary to use a boron doped gate electrode for realizing a surface channel type and to make a thin gate insulating film.
As the gate insulating film is thinned, a phenomenon is likely to occur that boron ions doped into the gate electrode pass through the gate insulating film and reach the substrate channel region. It is known that in order to prevent this phenomenon, it is effective to use an oxynitride film as the gate insulating film.
Shallow trench isolation (STI) instead of LOCOS isolation has been proposed in order to manufacture high integration semiconductor devices. For the shallow trench isolation, a process of forming shallow grooves (trenches) in a wafer surface and then filling the insides of trenches with insulating material is performed before forming semiconductor elements. As a result, the active region surrounded by the isolation region has a convex cross sectional structure.
A thermal oxidation film to be formed on the convex area has stress so that the insulating film becomes hard to be grown, i.e., a thinning phenomenon occurs. If the thinning phenomenon occurs, it is difficult to make the thickness of a gate insulating film formed in the active region have reliably a constant value. In order to prevent the thinning phenomenon, it is known that wet oxidation is effective.
As compared to dry oxidation, wet oxidation provides a high oxidation speed so that it can effectively form an oxide film at a lower temperature. In order to form an oxynitride film through wet oxidation, base oxidation is first performed to form a thin oxide film, and then nitrogen is introduced into this oxide film.
For example, a wet oxide film is formed on a plurality of wafers at the same time in a vertical batch diffusion furnace, and thereafter nitrogen is introduced into the oxide film in the unit of wafer, i.e. wafer by wafer, by using a single wafer annealing system.
As described above, it is effective to use an oxynitride film as the gate insulating film in order to manufacture micro-channel MOS transistors having a high driving force. However, a manufacture process of forming a gate insulating film of a thin oxynitride film is complicated and the manufacture throughput lowers. Therefore, this process is not suitable for mass production.
It is desired to use NO or N2O as nitrogen containing gas when nitrogen is introduced into an oxide film. However, presently available systems are not capable of using such gas.
It is an object of the present invention to provide a manufacture method or system for a semiconductor device capable of forming a thin oxynitride film with good mass productivity.
It is another object of the present invention to provide a manufacture method or system for a semiconductor device capable of introducing nitrogen by using NO or N2O.
According to one aspect of the present invention, there is provided a manufacture method for a semiconductor device comprising the steps of: (a) transporting a silicon wafer into a reaction chamber having at least first and second gas introducing inlet ports and sealing the reaction chamber with an O-ring; (b) after said step (a), introducing an oxidizing atmosphere into the reaction chamber via the first gas introducing inlet port and raising a temperature of the silicon wafer to an oxidation temperature while the reaction chamber is maintained in the oxidizing atmosphere; (c) after said step (b), introducing a wet oxidizing atmosphere into the reaction chamber via the first gas introducing inlet port while the oxidation temperature is retained, to form a thermal oxide film on a surface of the silicon wafer; (d) after said step (c), purging gas in the reaction chamber by using inert gas to lower a residual water concentration to about 1000 ppm or lower; and (e) after said step (d), introducing an NO or N2O containing atmosphere into the reaction chamber via the second gas introducing inlet port while the silicon wafer is maintained at an annealing temperature which is at 700xc2x0 C. or higher and higher than the oxidation temperature, to introduce nitrogen into the thermal oxide film and to form an oxynitride film.
According to another aspect of the present invention, there is provided a manufacture system for a semiconductor device comprising: a reaction chamber; a first gas introducing path communicating with an internal space of said reaction chamber; a second gas introducing path communicating with an internal space of said reaction chamber at a position different from said first gas introducing path; and a gas flow check valve provided to each of said first and second gas introducing paths.
It is desired to perform wet oxidation and nitrogen introduction in the same chamber in order to form a thin oxynitride film with good mass productivity. However, during the process of wet oxidation and nitrogen introduction in the same chamber, the nitrogen containing gas may be mixed with water content or O2.
If NO or N2O is used as the nitrogen containing gas, nitric acid may be formed with a higher possibility when the gas is mixed with water content or O2. If the nitric acid formed in the chamber flows back and diffuses into a gas pipe, the metal of the gas pipe may be corroded.
It is possible to prevent mixture of a wet oxidizing atmosphere and a nitrogen introducing atmosphere and form a good oxynitride film, by separating processes and sufficiently purging gas in a reaction chamber by using inert gas at the intermediate processes.
As above, a thin oxynitride film of a high quality can be manufactured efficiently.